The aim of our research was to investigate the effect of a small nanocellulose (NC) addition on an improvement of the mechanical properties of epoxy composites. A procedure of chemical extraction from pressed lignin was used to obtain nanocellulose fibers. The presence of nanoparticles in the cellulose pulp was confirmed by FTIR/ATR spectra as well as measurement of nanocellulose particle size using a Zetasizer analyzer. Epoxy composites with NC contents from 0.5% to 1.5% w/w were prepared. The obtained composites were subjected to strength tests, such as impact strength (IS) and resistance to three-point bending with a determination of critical stress intensity factor (Kc). The impact strength of nanocellulose composites doubled in comparison to the unmodified epoxy resin (EP 0). Moreover, Kc was increased by approximately 50% and 70% for the 1.5 and 0.5% w/w NC, respectively. The maximum value of stress at break was achieved at 1% NC concentration in EP and it was 15% higher than that for unmodified epoxy resin. The highest value of destruction energy was characterized by the composition with 0.5% NC and corresponds to the increase of 102% in comparison with EP 0. Based on the analysis of the results it was noted that satisfactory improvement of the mechanical properties of the composite was achieved with a very small addition of nanofiller while other research indicates the need to add much more nanocellulose. It is also expected that this kind of use of raw materials will allow increasing the economic efficiency of the nanocomposite preparation process. Moreover, nanocomposites obtained in this way can be applied as elements of machines or as a modified epoxy matrix for sandwich composites, enabling production of the structure material with reduced weight but improved mechanical properties.

The article presents the results of research on the modification of Epidian 5 epoxy resin by introducing natural modifiers. It's easy accessibility and biodegradability has a positive effect on environmental protection, cost-effectiveness of the process, useful and strength properties of composites. Still looking for the best solutions in the production of epoxy composites combining these features, we have attempted to compare and select the most optimal natural modifier. The epoxy resin was modified with collagen, hemp fibres, cellulose from pepper extraction residues. The amount of amine hardener suggested by the manufacturer was added to the composition. Each composition was cured at room temperature for 24 hours and then cured at 80°C for 3 hours. The prepared composites were subjected to impact assessment additions for mechanical properties, impact strength, three-point bending strength, critical stress intensity factor and gel time.